Color picture tube

ABSTRACT

A color picture tube includes a panel of which substantially rectangular effective area has a flat external surface and a curved internal surface, and on the internal surface of the effective area thereof a phosphor screen is formed. The internal surface of the effective area of the panel, when an average radius of curvature in major axis direction is RH, an average radius of curvature in minor axis direction is RV, an average radius of curvature in long side direction is RL and an average radius of curvature in short side direction is RS, is formed in a curved face satisfying RH&gt;RV and RS&gt;=RV, or RH&gt;RV and RS&gt;=RV and RL&gt;=RH. In this color picture tube, flatness of the effective area of the panel and visibility are improved.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a color picture tube, in particular toa color picture tube in which flatness of an image display portion andvisibility is improved.

(2) Description of Related Art

In general, a color picture tube that is employed in a TV Braun tube,computer display or the like has a vacuum envelope consisting of a glasspanel and a glass funnel of funnel shape. On an internal surface of theeffective area that is an image display portion of the panel, a phosphorscreen comprising phosphor layers of three colors, blue (B), green (G)and red (R), is formed. Electron beams emitted from electron guns thatare disposed inside the neck of the funnel are deflected by a magneticfield generated by a deflection yoke disposed outside the funnel to scanthe phosphor screen in a horizontal and vertical direction through ashadow mask, resulting in a display of color images.

The panel of the color picture tube comprises an effective area whoseplane shape is essentially rectangular and a sidewall disposed in thesurrounding area thereof. So as to obtain strength capable of supportingthe weight of atmosphere applied on the vacuum envelope, the internaland external surfaces of the panel are formed with different curvatures,and the thickness thereof is formed to become thicker from the centerportion of the effective area towards a periphery portion thereof.

In recent years, in order to improve visibility of images, the externalsurface of the effective area of the panel is being made flat(flattening). In order to improve the visibility, it is also necessaryfor the internal surface of the effective area to be flat. Nevertheless,in order to secure strength to support the curved surface of a shadowmask disposed inside the panel and strength of the vacuum envelopesupporting atmospheric pressure, it had been extremely difficult to makethe internal surface of the effective area of the panel flat to thelevel comparable with the external surface. In addition, from aviewpoint of the characteristics of a color picture tube, it wasdifficult to make the internal surface of the effective area flat.

Further, a phosphor screen is formed in contact with the internalsurface of the effective area of the panel. The substantial imagedisplay portion is, when not taking into account the refractive index ofthe glass panel, a curved face that is the same as the internal surfaceof the effective area. Accordingly, so far there was a problem thatimages of high flatness could not be obtained without making theinternal surface flat.

SUMMARY OF THE INVENTION

An object of the present invention is that in a color picture tube wherethe effective area of a panel is substantially rectangular, the internalsurface of the effective area thereof is formed in a curved face havingimproved visibility to attain a better sense of flatness of images. Atthe same time, the strength that supports a curved surface of a shadowmask is secured and deterioration of color purity due to local thermalexpansion of the shadow mask is prevented from occurring.

The present invention is a color picture tube, comprising a transparentpanel of which an external surface is flat, and an internal surface is acurved face and a plane shape with a substantially rectangular effectivearea, and a phosphor screen disposed on the internal surface of theeffective area of the panel, wherein RH>RV and RS≧RV, where RH is anaverage radius of curvature in major axis direction and denotes a radiusof a curved line (an arc) that goes through a center of the internalsurface of the effective area and ends on a major axis, RV is an averageradius of curvature in minor axis direction and denotes a radius of anarc that goes through the center and ends of a minor axis on theinternal surface of the effective area, and RS is an average radius ofcurvature in short side direction and denotes a radius of an arc thatgoes through an end of the major axis and ends of diagonal axes on theinternal surface of the effective area.

Further, in the color picture tube according to the present invention,the internal surface of the effective area can be formed with a curvedface that satisfies the following expressions (1), (2) and (3).

RH>RV  (1)

RS≧RV  (2)

RL≧RH  (3)

Here RL is an average radius of curvature in long side direction anddenotes a radius of an arc that goes through an end of the minor axisand ends of the diagonal axes of the internal surface of the effectivearea.

In addition, the internal surface of the effective area can be formedwith a curved face in which long sides that go through the end on theminor axis and the ends on the diagonal axes exist approximately on oneplane.

Further, in a color picture tube in which the internal surface of theeffective area of the panel satisfies all the aforementioned expressions(1), (2) and (3),

wherein the internal surface of the effective area can be formed with acurved face that further satisfies the following expressions (4) and(5).

2<RH/RV<15  (4)

1<RH/RD<10  (5)

Incidentally, RD is an average radius of curvature in diagonal axisdirection and denotes a radius of an arc that goes through the centerand the ends of the diagonal axes of the internal surface of theeffective area.

Further, in such a color picture tube, the internal surface of theeffective area can be formed with a curved face that satisfies thefollowing expression (6).

 1<RS/RV<5  (6)

Still further, the internal surface of the effective area can be formedin a curved face that satisfies the following expression (7).

3<RL/RH  (7)

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing, with a cross-section, a schematic structureof a first embodiment of the present invention,

FIG. 2 is a diagram schematically showing a shape of an internal surfaceof an effective area of a panel in the first embodiment,

FIG. 3 is a diagram schematically showing a shape of an internal surfaceof an effective area of a panel in a second embodiment of the presentinvention, and

FIG. 4 is a diagram schematically showing a shape of an internal surfaceof an effective area of a panel of an existing color picture tube.

DETAILED DESCRIPTION OF THE INVENTION

A color picture tube of the present invention, as shown in FIG. 1,comprises a vacuum envelope consisting of a glass panel 1 and a glassfunnel 2 having the shape of a funnel, one end of the funnel 2 being acylindrical neck 3. The panel 1 comprises an effective area 1 a and asidewall 1 b disposed in the periphery thereof, the effective area 1 aof the panel 1 being substantially rectangular in which a horizontalaxis (X axis) crossing at a right angle with a tube axis (Z axis) is themajor axis and a vertical axis (Y axis) crossing at a right angle withthe tube axis is the minor axis.

Further, an external surface of the effective area 1 a is approximatelyflat. However, the internal surface thereof is formed in a curved facethat is expressed by a polynomial of higher order in which an averageradius of curvature in major axis direction RH, an average radius ofcurvature in minor axis direction RV, an average radius of curvature inlong side direction RL, an average radius of curvature in short sidedirection RS, and an average radius of curvature in diagonal axisdirection RD satisfy the aforementioned expressions (1) through (7),respectively. Incidentally, in the present invention, that the externalsurface of the effective area 1 a is approximately flat means that theaverage radius of curvature in diagonal axis direction is 10000 mm ormore.

On the internal surface of the effective area 1 a of the panel 1, aphosphor screen 4 comprising phosphor layers of three colors, blue (B),green (G) and red (R), is formed. Further, at a position a prescribeddistance inwards of the phosphor screen 4, a shadow mask 5 consisting ofa mask body 5 a and a mask frame 5 b set in the periphery of the maskbody 5 a is disposed. The mask body 5 a is substantially rectangular andhas a lot of holes electron beams go through in an effective surfaceconsisting of a curved surface that faces the phosphor screen 4.

On the other hand, inside the neck 3 of the funnel 2, electron guns 7that emit three electron beams 6 are disposed. The beams are arranged ina row that goes through the same horizontal plane. The electron beams 6are deflected by a magnetic field generated by a deflection yoke 8attached outside of the funnel 2. The deflected electron beams 6 scanthe phosphor screen 4 in horizontal and vertical directions throughholes of the shadow mask 5 that allow the electron beams to pass.Thereby, color images can be displayed.

In the color picture tube of the present invention, the internal surfaceof the effective area has a curved face to satisfy the followingexpressions.

RH>RV  (1)

RS≧RV  (2)

This is due to the following reasons.

First, as a model of curved face of the internal surface of theeffective area, three models, that is, a major axis directioncylindrical surface that shows a cylindrical shape in the major axis (Xaxis) direction, a spherical surface, and a minor axis directioncylindrical surface that shows a cylindrical shape in the minor axis (Yaxis) direction can be thought of With the amount of drop-off in tubeaxis (Z axis) direction maintained the same at the ends of the diagonalaxes, the strengths of the curved faces are compared. In the sphericalsurface, over the entire surface, the strength is approximately thesame. In the major axis direction cylindrical surface and minor axisdirection cylindrical surface, the strengths are identical at thecenters of the curved surfaces. However, the respective strengths at anintermediate area of the major axis direction and an intermediate areaof the minor axis direction are remarkably weak compared with that ofthe center.

On the other hand, local thermal expansion of a shadow mask, in theorder of the minor axis direction cylindrical surface, the sphericalsurface and the major axis direction cylindrical surface, becomeslarger. When calculated in terms of amount of shift of an electron beamon a screen surface, with the shift of the minor axis directioncylindrical surface being 1, the shift of the spherical surface is 2,and the shift of the major axis direction cylindrical surface is 4.Accordingly, from both of the strength of a curved surface of a shadowmask and, suppression of deterioration of color purity due to localthermal expansion thereof, a curved face that is an intermediate ofspherical surface and minor axis direction cylindrical surface isexpected to be preferable.

Further, when RH<RV, RH is made sufficiently large with difficulty. Inthe case of the value of RH being not large, when the screen (effectivearea of a panel) is seen from the side, the opposite side of the screencan not be seen due to the convex center portion. Accordingly, flatimages can not be displayed. In addition, an effective dimension in thehorizontal axis (major axis) direction of the effective area of a panelis larger than that in vertical axis (minor axis) direction.Accordingly, when the value of RH is small, such as approximately 1300mm, the thickness of the surrounding area in the horizontal direction ofthe panel increases. As a result of this, the panel is formed withdifficulty, and its fabrication is not practical.

On the other hand, when the value of RH is large (for exampleapproximately 18000 mm), if the value of RV is made larger than that ofRH, it becomes difficult to obtain a shadow mask having strengthsufficient for supporting a curved surface. That is, the shape of theeffective surface of the shadow mask, in the case of value of the RVbeing 18000 mm or more to conform to the shape of the internal surfaceof the effective area of the panel, has insufficient strength to supportthe curved surface of the shadow mask. This is not desirable.

Further, in order to prevent deterioration of color purity due tothermal expansion by increasing the strength supporting the curvedsurface of the shadow mask, the average radius of curvature RS in shortside direction of the internal surface of the effective area of a panelis preferable to be equal with or larger than the average radius ofcurvature in minor axis direction RV (RS≧RV). From the viewpoint ofimprovement of sense of flatness, the value of RS is preferable to be aslarge as possible. However, from the viewpoint of suppression ofdeterioration of the color purity due to the thermal expansion of theshadow mask, the value of RS is preferable to be small. Further, whenthe values of RS are the same, by forming the center portion of theshort side in convex towards the center of the effective area, the senseof flatness is known to be improved (cf. Japanese Patent Application No.10-40583). The shape of the internal surface of the effective area of apanel and the strength supporting the curved surface of a shadow maskwill be explained in more detail.

In a shadow mask type color picture tube, from the operation principlethereof, a shadow mask is required to be disposed a definite distanceaway from an internal surface of a panel. Accordingly, in order tomaintain the shape of the shadow mask consisting of a thin iron plate orInvar material having a low thermal expansion coefficient, in particularin the shadow masks that are produced by the use of presswork, the shapethereof must be formed in a curved surface.

Further, by increasing the pitch of holes which electron beams passthrough from the center portion of the shadow mask towards thesurrounding portion thereof, even when the internal surface of the panelis made flat, the effective surface of the shadow mask can be formed ina curved surface with a large radius of curvature. However, since thepitch of the holes influences resolution power of a color picture tube,the variation rate of the pitch is preferable not to be larger than acertain degree. Further, recently, since the pitch of the holes that thebeam pass through is required to be uniform up from the center portionto a periphery portion, the internal surface of the panel and the shadowmask are required to be curved surfaces having the same radii ofcurvature.

Thus, the internal surface of the panel must be a curved face that cangive a sufficient degree of strength to support the shadow mask disposedopposite thereto. Furthermore, since color purity of images isdeteriorated due to local thermal expansion of the shadow mask, in orderto prevent the deterioration of the color purity from occurring, theinternal surface of the effective area of the panel must be formed in acurved face having a certain degree of radius of curvature, particularlyin major axis direction.

As described above, in a color picture tube of the present invention, inaddition to an external surface of the effective area of a panel beingflat, an internal surface thereof is formed in a curved face satisfyingthe aforementioned expressions (1) and (2). Accordingly, the strength ofvacuum envelope against atmospheric pressure is maintained high and,compared with the existing color picture tube, images of improvedvisibility and sense of flatness can be displayed. In addition, thestrength supporting the curved surface of the shadow mask is maintainedhigh and deterioration of the color purity due to thermal expansion ofthe shadow mask can be prevented from occurring. Thus, a color picturetube of high display quality can be realized.

Further, in the present invention, the following expression (3) ispreferable to be satisfied.

RL≧RH  (3).

When the average radius of curvature in long side direction RL is largerthan or equal with the average radius of curvature in major axisdirection RH, the long side of the effective area of the panel becomesapproximately a straight line unrelated to the angle viewing the screen.Accordingly, the sense of flatness of the screen can be improvedfurther.

Further, in the present invention, an internal surface of the effectivearea of a panel is preferred to be a curved face satisfying thefollowing expressions

2<RH/RV<15  (4)

and

1<RH/RD<10  (5),

and further preferred to satisfy at least one of the followingexpressions (6) and (7).

1≦RS/RV<5  (6)

3<RL/RH  (7)

The preferable ranges shown in the expressions (4) and (5) are necessaryand sufficient for preventing deterioration of color purity due to localthermal expansion of a shadow mask and the difference of the panelthicknesses of the center portion and the periphery from becoming toolarge. When the value of RH/RV is 2 or less, or the value of RH/RD is 1or less, the deterioration of the color purity due to the local thermalexpansion of the shadow mask can not be sufficiently prevented. On thecontrary, when the value of RH/RV exceeds 15, or the value of RH/RDexceeds 10, the differences of the thicknesses between the end in minoraxis direction and the end in major axis direction, and the end in majoraxis direction and the end in diagonal axis direction become too large.

The expression (6) (1≦RS/RV<5) is a condition required from flatness ofthe screen. That is, when the screen (effective area of a panel) is seenfrom the side, in order for the visibility of the short side not todamage the flatness, the value of RS/RV is necessary to be 1 or more(RS≧RV). Further, when the value of RS/RV is made 5 or more, the localthermal expansion of the shadow mask becomes large, resulting indeterioration of the color purity of the screen. This is not desirable.

In order to improve flatness, 3<RL/RH is preferable. That is, in orderto enhance further the sense of flatness of the screen, in the internalsurface of the effective area of a panel, it is desirable to set thevalue of RL at 15000 mm or more and to make the long side a straightline on approximately the same plane. When the internal surface is acurved face close to spherical surface, since the value of RH becomes5000 mm at the maximum, to make the long side an approximate straightline, the preferable range of the value of RL/RH is 3 or more.

In the following, preferred embodiments of the present invention will beexplained in more detail. Incidentally, the present invention is notrestricted to the following embodiments.

Embodiment 1

In a color picture tube of which an aspect ratio of breadth and heightis 16:9 and a diagonal dimension is 76 cm, an external surface of aneffective area of a panel is made approximately flat (average radius ofcurvature in diagonal axis direction is 10000 mm or more), and aninternal surface thereof is formed in a curved face expressed by apolynomial of higher order. The shape of this curved face is shownschematically in FIG. 2. For comparison purpose, the shape of aninternal surface of an effective area of a panel of an existing colorpicture tube is shown in FIG. 4.

In the internal surface of the effective area of the panel, with acenter C as the origin of the coordinate axes, coordinates (x, y, z) ofan end point H of a major axis (X-axis), an end point V of a minor axis(Y-axis) and an end point D of a diagonal axis are shown in Table 1,respectively. Incidentally, minus signs of z-values of the respectiveend points H, V and D show that the respective end points H, V and Ddrop off with respect to the center C in a direction perpendicular tothe plane of the paper.

TABLE 1 Coordinate (mm) (x, y, z) Horizontal axis Vertical axis end(major axis end (minor Diagonal axis Center C end) H axis end) V end D(0, 0, 0) (330, 0, −5) (0, 186, −13) (330, 186, −17)

Further, average radii of curvature in major axis direction RH, in minoraxis direction RV, in long side direction RL, and in short sidedirection RS are shown in Table 2, respectively.

TABLE 2 Average radius of curvature (mm) RH RL RV RS 10893 13656 13371448

As shown in Table 2, in the panel of the color picture tube ofEmbodiment 1, the internal surface of the effective area is a curvedface that satisfies all of the following expressions.

RH>RV  (1)

RS≧RV  (2)

RL≧RH  (3)

As a result of this, the color picture tube, in addition to the externalsurface being flat, is further improved in visibility and can displayimages with an excellent sense of flatness. In addition, since strengthsupporting a curved surface of a shadow mask can be maintainedsufficiently large and deterioration of the color purity due to thermalexpansion is prevented from occurring, images of high quality can bedisplayed.

Embodiment 2

As in embodiment 1, in a color picture tube of which an aspect ratio ofbreadth and height is 16:9 and a diagonal dimension is 76 cm, anexternal surface of an effective area of a panel is made approximatelyflat, and an internal surface thereof is formed in a curved face that isexpressed by a polynomial of higher order shown in FIG. 3.

In the internal surface of the effective area of the panel, with thecenter C as the origin of the coordinate axes, coordinates (x, y, z) ofan end point H of a major axis, an end point V of a minor axis and anend point D of a diagonal axis are shown in Table 3, respectively.

TABLE 3 Coordinate (mm) (x, y, z) Center C Major axis end H Minor axisend V Diagonal axis end D (0, 0, 0) (330, 0, −3) (0, 186, −16) (330,186, −17)

Further, the average radii of curvature in major axis direction RH, inminor axis direction RV, in long side direction RL and in short sidedirection RS are shown in Table 4, respectively.

TABLE 4 Average radius of curvature (mm) RH RL RV RS 18152 54616 10891243

As shown in Table 4, in the panel of the color picture tube ofEmbodiment 2, the internal surface of the effective area is a curvedface that satisfies all of the above expressions (1) through (3). Inparticular in this embodiment, the internal surface of the effectivearea is formed in a shape that has thickness difference of the panel of1 mm on the long side.

Further, when the difference of coordinates on the long side in tubeaxis direction is approximately 2 mm, the long side can be locatedapproximately on the same plane. As shown in Table 3, in the panel ofthe present embodiment, since the difference of the coordinates in thetube axis direction of the minor axis end point V and the diagonal axisend point D is 1 mm (17 mm−16 mm), the long side is approximately on thesame plane and forms a straight line. By the way, the difference ofcoordinates in tube axis direction of the major axis end point H anddiagonal axis end point D is as large as 14 mm (17 mm−3 mm).Accordingly, the short side is not on the same plane.

Thus, in the color picture tube of Embodiment 2, the internal surface ofthe effective area of the panel is formed in a curved face as describedabove and the long side is approximately on the same plane. Accordingly,the flatness is further improved and the visibility is improved. Inaddition, compared with the color picture tube of Embodiment 1, a shadowmask can be formed in a curved surface of larger strength for supportingthe curved surface. Accordingly, deterioration of color purity due tothermal expansion of the shadow mask can be prevented from occurring.

Embodiment 3

As in embodiment 1, in a color picture tube of which an aspect ratio ofbreadth and height is 16:9 and a diagonal dimension is 76 cm, anexternal surface of an effective area of a panel is made approximatelyflat, and an internal surface thereof is formed in a curved faceexpressed by a polynomial of higher order.

In the internal surface of the effective area of the panel, with thecenter C as the origin of the coordinate axes, coordinates (x, y, z) ofan end point of a major axis H, an end point of a minor axis V and anend point of a diagonal axis D are shown in Table 5, respectively.

TABLE 5 Coordinate (mm) (x, y, z) Center C Major axis end H Minor axisend V Diagonal axis end D (0, 0, 0) (331, 0, −8) (0, 186, −12) (331,186, −13)

Further, at this time, the average radii of curvature in major axisdirection RH, in minor axis direction RV, in long side direction RL, inshort side direction RS, and in diagonal axis direction RD are obtained,respectively. In addition, the values of ratios of the respectiveaverage radii of curvature (RH/RV, RH/RD, RL/RH and RS/RV) arecalculated, respectively. These results are shown in Table 6.

TABLE 6 Average radius of curvature (mm) RH RL RV RS RD 6852 54781 14483462 5551 Ratio of average radii of curvature RH/RV RH/RD RL/RH RS/RV4.7 1.2 8.0 2.4

As shown in Table 6, in the panel of the color picture tube ofEmbodiment 3, the internal surface of the effective area is a curvedface that satisfies all of the following expressions.

2<RH/RV<15  (4)

1<RH/RD<10  (5)

1≦RS/RV<5  (6)

3<RL/RH  (7)

Accordingly, the panel of Embodiment 3, in addition to having a flatexternal surface, is further improved in visibility and can displayimages of excellent sense of flatness. Further, the strength supportingthe curved surface of a shadow mask is kept sufficiently large and thecolor purity is prevented from deteriorating due to thermal expansion.Accordingly, images of excellent quality can be displayed. Further, inthe panel of the color picture tube, when the screen is seen from anoblique direction of an angle of view of 45°, the short side is seen asa curved line that is convex towards outside of the effective area andhas a sufficiently large radius of curvature (radius of curvature R isapproximately 18700 mm). Accordingly, a satisfying sense of flatness ofthe screen can be obtained.

Embodiment 4

In a color picture tube of which an aspect ratio of breadth and heightis 4:3 and a diagonal dimension is 68 cm, an external surface of aneffective area of a panel is made approximately flat, and an internalsurface thereof is formed in a curved face expressed by a polynomial ofhigher order.

In the internal surface of the effective area of the panel, with thecenter C as the origin of the coordinate axes, coordinates (x, y, z) ofan end point of a major axis H, an end point of a minor axis V and anend point of a diagonal axis D are shown in Table 7, respectively.

TABLE 7 Coordinate (mm) (x, y, z) Center C Major axis end H Minor axisend V Diagonal axis end D (0, 0, 0) 272, 0, −8) (0, 204, −13) (204, 186,−14)

Further, an average radii of curvature in major axis direction RH, inminor axis direction RV, in long side direction RL, in short sidedirection RS, and in diagonal axis direction RD are obtained,respectively. In addition, the values of ratios of the respectiveaverage radii of curvature (RH/RV, RH/RD, RL/RH and RS/RV) arecalculated, respectively. These results are shown in Table 8.

TABLE 8 Average radius of curvature (mm) RH RL RV RS RD 6628 36978 16073471 4136 Ratio of average radii of curvature RH/RV RR/RD RL/RH RS/RV2.88 1.12 7.99 2.16

As shown in Table 8, in the panel of the color picture tube ofEmbodiment 4, the internal surface of the effective area is, as inEmbodiment 3, a curved face that satisfies all of the aforementionedexpressions (4) through (7). Accordingly, the panel of Embodiment 4 hasa flat external surface and the visibility thereof is further improved.The strength supporting the curved surface of a shadow mask is keptsufficiently large and the color purity is prevented from deterioratingdue to thermal expansion.

Accordingly, images of excellent quality can be displayed. Further, inthe panel of the color picture tube, when the screen is seen from anoblique direction with an angle of view of 45°, the short side is seenas a curved line that is convex towards outside of the effective areaand has a sufficiently large radius of curvature (radius of curvature Ris approximately 18500 mm). Accordingly, a satisfying sense of flatnessof the screen can be obtained.

As obvious from the above description, according to the presentinvention, an internal surface of an effective area of a panel can beformed in a curved face satisfying the following expressions,

RH>RV and RS≧RV

or

RH>RV and RS≧RV and further RL≧RH.

Accordingly, in addition to the strength of vacuum envelope againstatmospheric pressure being maintained sufficiently high, the visibilityof images is improved and the images are displayed with a sense offlatness. In addition, the strength supporting a curved surface of ashadow mask is maintained high enough and deterioration of the colorpurity due to thermal expansion of the shadow mask can be prevented fromoccurring.

Further, in the present invention, the ratios of average radii ofcurvature of the internal surface of the effective area are restrictedin the ranges of

2<RH/RV<15 and 1<RH/RD<10.

Thereby, in particular when seen from an oblique direction, the flatnessof the screen can be further improved.

What is claimed is:
 1. A color picture tube, comprising: a transparentpanel of which external surface is flat and internal surface is a curvedface and plane shape has a substantially rectangular effective area; anda phosphor screen disposed on the internal surface of the effective areaof the panel; wherein RH>RV, RS≧RV, 2<RH/RV<15 and 1<RH/RD<10, where RHis an average radius of curvature in major axis direction and denotes aradius of an arc that goes through a center of the internal surface ofthe effective area and ends on a major axis, RV is an average radius ofcurvature in minor axis direction and denotes a radius of an arc thatgoes through the center and ends of a minor axis on the internal surfaceof the effective area, RS is an average radius of curvature in shortside direction and denotes a radius of an arc that goes through an endof the major axis and ends of diagonal axes on the internal surface ofthe effective area, and RD is an average radius of curvature in diagonalaxis direction and denotes a radius of an arc that goes through thecenter and the ends of the diagonal axes of the internal surface of theeffective area.
 2. The color picture tube as set forth in claim 1:wherein RL≧RH, where RL is an average radius of curvature in long sidedirection and denotes a radius of an arc that goes through an end of theminor axis and ends of the diagonal axes of the internal surface of theeffective area.
 3. The color picture tube as set forth in claim 1:wherein, in the internal surface of the effective area, long sides thatgo through the end of the minor axis and the ends of the diagonal axesexist approximately on a plane.
 4. The color picture tube as set forthin claim 1: wherein 1≦RS/RV<5.
 5. The color picture tube as set forth inclaim 2: wherein 3<RL/RH.